Many polysaccharides can exist in acetylated forms in various biological plant materials (mainly in xylan, mannan and pectin polymers) [1]. The biological significance of the acetyl groups is not fully understood. It is known that the acetyl group often protects the polysaccharide from degradation by hydrolytic enzymes. Hence, deacetylation of these polysaccharides is necessary in order to achieve partial or complete enzymatic breakdown of the acetylated polysaccharide [2-4].
Accordingly, it is contemplated [2,3] that acetyl esterases are important enzymes for the food industry, primarily in fruit and vegetable processing such as fruit juice production, wine making or pectin extraction, where their ability to modify acetylated polysaccharides to a readily degradable form may be utilised.
It is known that many fungi contain enzymes capable of deacetylating acetylated polysaccharides, which enzymes are commonly designated acetyl esterases. Some fungal acetyl esterases have been purified [5-9]. However, the study of these enzymes have been hampered by the lack of well-characterized homogeneous substrates, and by the difficult and time consuming assays for measuring acetate release. Any industrial use of hese enzymes has not been described.
WO 92/19728 describes a rhamnogalacturonan acetyl esterase isolated from the fungal species Aspergillus aculeatus. This enzyme is specific for acetylated galacturonic acid residues in hairy regions of pectin. EP 507 369 discloses a DNA sequence encoding an acetyl xylan esterase isolated from Aspergillus niger.
For many purposes, it would be desirable to provide acetyl esterases in a form essentially free from other components. In this way, it would be possible to produce enzyme preparations adapted to specific purposes, such preparations either containing a single acetyl esterase or arbitrary combinations thereof, and optionally containing other polysaccharide degrading enzymes. To serve this end, it is convenient to provide single-component acetyl esterases by recombinant DNA techniques.